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<div class="moz-cite-prefix">Hi Andreas,<br>
I was hoping the QGIS project would keep the definition of the
virtual fields - at least until I exited QGIS - and then by
re-opening the same SHP file, I hoped for a reconnection of
virtual fields. Yes, I know it's not that simple, but exploring
QGISes abilities is what I am playing with now.<br>
<br>
Thanks for the pointer to 'Save Layer Definition file' - I've
never noticed that, so I'll play with that for a bit.<br>
<br>
Thanks to Matthias too for his comments.<br>
Yes, it is a bummer that you can only generate virtual content <u>dynamically</u>
with the FC (and SHP files).<br>
<br>
Hopefully not to open a can of worms, but I can't see any reason
why QGIS cannot create some sort of information/status/whatever
file by using a '.Qstuff' type file extension stored with the SHP
file name. This would not interfere with other SW using SHP files,
and would greatly enhance QGIS's ability in processing this
(really hateful) file format.<br>
I abhor SHP file format, but it has unfortunately become the de
facto request from clients, so it would be nice to have more
advanced processing capabilities for this format.<br>
<br>
Regards & have a good weekend.<br>
Zoltan<br>
<br>
<br>
On 2014/11/07 18:59, Andreas Neumann wrote:<br>
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Hi Zoltan,<br>
<br>
If you remove and re-add the shapefile you will of course loose
the virtual fields, as they are stored with the project and not
with the data.<br>
<br>
However, if you save a layer definition file along with the
shapefile and re-add that, they are preserved. So you can just
store the layer definition file along with the shape and you are
fine to share the data with your colleagues, preserving virtual
fields ;-)<br>
<br>
Andreas<br>
<br>
<div class="moz-cite-prefix">On 07.11.2014 17:32, Zoltan Szecsei
wrote:<br>
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<div class="moz-cite-prefix">Hi Andreas,<br>
I'll fiddle with the Postgis idea - thanks.<br>
The orange part below:<br>
I closed the shapefile, deleted from legend and re-opened it -
but could not see my virtual field, nor the expression I used
to create it.<br>
Have I missed a trick somewhere?<br>
<br>
Regards,<br>
Z<br>
<br>
On 2014/11/07 18:25, Andreas Neumann wrote:<br>
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Hi,<br>
<br>
What you probably ask for are database triggers combined with
storage. This is not what virtual fields are for. If they were
stored - they wouldn't be called virtual ;-)<br>
<br>
You can do that f.e. with Postgis. With shapefiles not. <font
color="#ff6600">However, if you share the project with the
other PC, the virtual fields work fine</font>.<br>
<br>
Andreas<br>
<br>
<div class="moz-cite-prefix">On 07.11.2014 17:21, Zoltan
Szecsei wrote:<br>
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type="cite">
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<div class="moz-cite-prefix">Hi Matthias,<br>
Thanks for the quick answer.<br>
The virtual field acts just like I want it to, except that
it does not permanently store the column in the attribute
table.<br>
I tried getting clever by then adding a second 'Field
Calculation' to update the existing 'Sheet' field from the
virtual field, but that won't do it either.<br>
<br>
So, for me there are two shortcomings:<br>
<ol>
<li>To be able to store and recall the 'Expression' and
not lose it after closing the Field Calculator</li>
<li>To be able to add the virtual fields that you
create, into the attribute table.</li>
<li>(And then of course to re-open the Shape file on
another PC and have these Field Calculations still
functional)<br>
</li>
</ol>
Any further possibilities I can try?<br>
<br>
Regards & thanks again,<br>
Zoltan<br>
<br>
<br>
On 2014/11/07 18:01, Matthias Kuhn wrote:<br>
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<blockquote cite="mid:545CECD7.9030808@gmx.ch" type="cite">
<pre wrap="">Hi Zoltan,
Since QGIS 2.6 this possibility exists. It is called "Virtual Field".
You must not create the attribute when creating the shapefile. Just open
the field calculator, create a new field in there and check the "virtual
field" checkbox.
Regards,
Matthias
On 07.11.2014 16:54, Zoltan Szecsei wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Hi,
I'm using QGIS 2.6.0 on Win 7 x64 - installed via OSGEO4w
Is there a way to store your field calculator expression to always
process and update that specific field, should geometry be edited or
created for that Layer?
Let's say I want to create a blank POINT shape file, with a text
attribute called "Sheet".
Whenever a POINT is created or moved, I want this field to be
dynamically updated with:
tostring(abs(toint($y)))+tostring(abs(toint($x)))
For testing thus far have:
* created 2 points
* Opened the field calculator, clicked 'Update Existing Field' and
put in the expression.
* The two existing points now have the correct TEXT values in the
Sheet field
* I close the Field calculator
* Create a new point in my layer
* open the attribute table to find that the 'Sheet' field for this
new point is blank
* I open the Field Calculator and I cannot even find a way to call
back the previous expression I used.
Am I using the correct QGIS functionality to achieve what I need to,
and if so, where am I going wrong?
Thanks & regards,
Zoltan
--
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GIS and Photogrammetric Services
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===========================================
Zoltan Szecsei PrGISc [PGP0031]
Geograph (Pty) Ltd.
GIS and Photogrammetric Services
P.O. Box 7, Muizenberg 7950, South Africa.
Mobile: +27-83-6004028
Fax: +27-86-6115323 <a moz-do-not-send="true" class="moz-txt-link-abbreviated" href="http://www.geograph.co.za">www.geograph.co.za</a>
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<pre class="moz-signature" cols="72">--
===========================================
Zoltan Szecsei PrGISc [PGP0031]
Geograph (Pty) Ltd.
GIS and Photogrammetric Services
P.O. Box 7, Muizenberg 7950, South Africa.
Mobile: +27-83-6004028
Fax: +27-86-6115323 <a moz-do-not-send="true" class="moz-txt-link-abbreviated" href="http://www.geograph.co.za">www.geograph.co.za</a>
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<pre class="moz-signature" cols="72">--
===========================================
Zoltan Szecsei PrGISc [PGP0031]
Geograph (Pty) Ltd.
GIS and Photogrammetric Services
P.O. Box 7, Muizenberg 7950, South Africa.
Mobile: +27-83-6004028
Fax: +27-86-6115323 <a class="moz-txt-link-abbreviated" href="http://www.geograph.co.za">www.geograph.co.za</a>
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